First of all, you are in for a real treat, because, in my opinion, the holidays are the best time to see
Disneyland. It is absolutely magical.
You didn't say where you would be staying when you are at Disneyland, but you should definitely check out the Grand Californian Hotel. Even if you don't stay there and just sit in the lounge area and sip a beverage, it is the perfect setting to soak up some holiday atmosphere. It is elegant but kind of rustic at the same time. The lobby is enormous, with dim lighting, dark wood and high ceilings. There is also a piano player. There is a beautiful Christmas tree in the center, and everyone gathers around it to hear the Christmas carolers sing every night. GCH is also home to the 4-star restaurant, Napa Rose, which YellowMickeyPonchos is very familiar with. It gets excellent reviews.
You won't find much in the way of real snow as far as the weather in Southern California (you would have to go to Big Bear or Lake Arrowhead for that!), but in DLR, there is the nightly 'snowfall' on Main Street (at designated times). The famous castle is adorned with 'snow' for the holidays but it is stunning to see at night, when it turns an almost incandescent blue-purple shade. As a previous poster said, It's a Small World Holiday cannot be missed. The exterior of the ride/building - especially at night - is absolutely breathtaking to behold. In fact, we rode IASWH a couple of times in the daytime and nobody was in line because I think people did not realize it was a holiday version of the ride. However, at night, it takes on a whole new life, and the beautiful, colored, twinkling lights acted like a beacon that seemed to attract visitors from all corners of the park. Suddenly the line for the ride was 45 minutes long. And the ride itself has been transformed to include holiday decorations, holiday songs and also the very faint whiff of peppermint as you sail through the 'candy cane factory.' You will also get to see the Haunted Mansion Holiday with the Nightmare Before Christmas theme. This ride has totally been revamped for the holiday as well, in great detail. Some people love it, some hate it, but I think we all can agree that the Disney folks certainly changed almost every detail of the regular Haunted Mansion ride to accommodate the Nightmare Before Christmas theme for three months!
Other than all this, there is unique holiday food, merchandise, characters in winter gear, decorations all over the parks - some themed to each land - and just an overall extra dose of Disney magic that transcends the usual magic we find when we go there. It is really a special time of the year, and I am so glad you will get to experience it! Whenever I hear that someone is going to experience Disneyland at Christmas for the first time ever, I get excited FOR them because I know how much they will love it!
So I am in the minority too. I am clamoring for Disney to open up an 'Arctic Adventure' park just for us COLD buffs!
We went the first week of December and they were making them two times during our vacation time. 
So, no candy canes for us. Oh well....
